This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Introduction: Self-injurious behavior (SIB) may be defined as any self-directed behavior that results in tissue injury. The condition occurs in approximately 5-13% of the captive rhesus macaque population with self-biting being the most common expression of the behavior. Additionally, SIB is a significant human health problem, which interestingly occurs in 4% of the general public. Currently, there are no widely accepted treatments for human or nonhuman primate SIB. However, studies with human and nonhuman primates have shown that therapeutic drugs used to treat alcoholism and drug abuse, such as oral naltrexone hydrochloride, are effective in reducing the occurrence of SIB. To date, there have been no studies examining the value of Vivitrol, a long-acting 30 day injectable naltrexone, for the treatment of human or nonhuman primate SIB. A focused study using Vivitrol for SIB may open the exploration of a novel use for Vivitrol in both research facilities and the general public. Methods: A total of twenty adult rhesus macaques (Macaca mulatta) with documented self-injurious behavior will be assigned to one of two groups. Group 1 (n=16): In the first four week treatment phase baseline behavior will be observed and coded according to an established ethogram. Two injections of Vivitrol will be administered with a four week interval between injections. Behavior will be observed and coded. Blood samples will be taken at the time of each Vivitrol injection and at seven day intervals until the end of the study for therapeutic range data analysis The final phase will be a second baseline behavior observation and coding period. Group 2 (n=4): A pharmacokinetic study will be performed with blood sampling occurring at 0, 2, and 8 hours and 1, 5, 7, 10, 14, 17, 21, 25, and 28 days.